Resistance to the action of Insulin on glucose metabolism, with ensuing compensatory hyperinsulinemia, is closely linked to essential hypertension. The decreased insulin sensitivity observed in hypertensive patients is present in both obese and non-obese subjects. Hyperinsulinemia has been found to increase sodium and water retention by the kidneys and to increase circulating levels of norepinephrine. It has also been shown to increase blood pressure by some authors, but not others. On the other hand, endothelin (ET), is a potent endogenous vasoconstrictor, produced by the endothelium. It is found in small amounts in plasma, compared to high levels in urine. Despite many studies in the literature on the subject, the roles played by ET and hyperinsulinemia in essential hypertension are still unclear. We are investigating: 1) the effects of hyperinsulinemia on blood pressure and on urinary excretion of endothelin (UETV) in normal volunteers and in salt sensitive and salt resistant hypertensive subjects. The euglycemic insulin clamp technique, developed by Dr. DeFronzo, is being used, to assess the degree of insulin resistance and provide a controlled hyperinsulinemic state.